Let’s say your friend invites you over because she has a surprise to show you. The surprise turns out to be a time machine.

Once you are over your shock that your pal has mastered time travel, the two of you take a few turns going back and forth through history witnessing important events and whatnot.

Finally, your friend wraps your adventures up by returning a little before the present. You’re surprised again when you watch her teach her younger self how to build the machine.

Wait! How can your friend use time travel to travel back to teach herself how to build the darn time machine?

What a paradox!

Exactly.

This time travel scenario is called the “Bootstrap Paradox,” because it shows an unending cause-and-effect loop with no defined origin of said time travel.

Another example of the Bootstrap Paradox is in the Terminator movies, where the artificial intelligence Skynet learns how to build Terminators after one comes back to the past and dies only to be studied.

Another potential logical problem with time travel is called the Grandfather Paradox where you go back in time to find your own grandfather, making it impossible for your existence to find your own grandfather.

This one is sort of tricky too, but let’s take a deeper look.

So, you invent a time machine and travel back in time to meet your grandfather before he has children. You accidentally step on a butterfly and change the course of history, which means your grandfather never meets your grandmother and therefore, one of your parents is never born. This creates a paradox because if your parent is never born, then you can’t exist to travel back in time and meet your grandfather in the first place.

It’s like a never-ending loop!

To put it simply, the Grandfather Paradox means that if you travel back in time and do something that prevents your own existence, you can’t go back in time to do it in the first place. So, you end up stuck in a time loop, which is about as fun as watching paint dry.

In other words, time travel can be a real headache, and it’s probably best to leave it to the sci-fi writers and not mess with the space-time continuum.

Or at least, that’s what my future self told me when I tried to invent a time machine in my garage.